Active diodes are used to replace (passive) diodes e.g. in applications in which a threshold voltage (cut-in voltage) in the forward direction of the diode is undesirable, such as in charging systems of mobile devices, for example. An example of a conventional active diode is shown in FIG. 5. This active diode 5 comprises a transistor 510 and a comparator 520, as well as appropriately chosen resistors 551, 553, if necessary. A control voltage depending on the polarity of a voltage drop across the transistor 510 is supplied to a control terminal of the transistor 510 by the comparator 520, wherein the control voltage is set to switch the transistor 510 fully on (fully conducting state) e.g. for positive voltage drop. However, the voltage drop across the transistor 510 becomes small once the transistor 510 is driven in the fully conducting state, which then may result in fluctuations of the control voltage that is output by the comparator 520, and consequently, in oscillations of the active diode 5. Measures to address this issue include employing low gain amplifiers instead of comparators to provide the control voltage for the transistor 510. This however results in less power efficient active diodes, since the low gain amplifiers require a larger voltage drop across the transistor 510 until the transistor 510 is switched fully on.